Electrical system of measuring temperatures.



No. 880,074. PATENTED FEB. 25, 1908. E. HAAGN.

ELECTRICAL SYSTEM OF MEASURING TEMPERATURES.

APPLICATION FILED MAY 27. 1907.

3 SHEETS-SHEET 1.

III aw 'IIH No. 880,074. PATENTED FEB. 25, 1908.

E. HAAGN. ELECTRICAL SYSTEM OF MEASURING TEMPERATURES.

APPLICATION FILED MAY 27. 1907.

3 SHEETS-SHEET 2.

No. 880,074. PATENTED FEB. 25, 1908. E. HAAGN. ELECTRICAL SYSTEM OFMEASURING TEMPERATURES.

APPLICATION FILED MAY 27. 190%.

3 SHEETSSHEET 3.

:. stones bridge.

ERNST HAAGN, OFHANAU, GERMANY,

ASSIGNOR 'ro FIRM or W. o. HERAEUS, or HANAU, GERMANY.

ELECTRICAL SYSTEM OF MEASURING TEMPERATURES.

, Specification of Letters Patent.

Patented Feb. 25, 1908.

Application filed lay 27.1907. Serial No. 375.989.

To all whom it may concern:

Be it known that I, ERNST HAAGN, a subject of the German Emperor, and aresident of Hanan, Germany, doctor of philosophy, have invented certainnew and useful Improvements in an Electric System of MeasurmgTemperatures, of which the following is a specification.

My invention relates to improvements in an electric system of measuringtempera tures, and more particularly to that class in which theresistance and thereby also the temperature indicated by a resistancethermometer is measured by means of Wheat- The systems of this classheretofore in use require an adjustment of the resistances of the bridgefor each temperature to be measured which method causes a considerableloss of time and furthermore cannot be executed by an unlearned laborer.Now, the object of my invention is tion, I have shown an example thereofin the.

accompanying drawings, in which Figure 1 is'a diagrammatical representation of the system, showing, as an example, means to obtain directmeasurements of any desired accuracy, Fig. 2 is a diagrammatical view ofa part of the system, showing means to balance variations of the voltageof the source of electricity, Fig. 3 is a dia ammatical representationof means to ba ance the resistance of the conductor including thethermometer, Fig. 4 is a diagrammatical view of a modification of themeans shown in Fig. 3 and Fig. 5, a dia rammatical view of a systemembodyin t e parts shown in Figs. 1 and 3. I

Similar letters of reference refer to similar parts in the. differentviews.

For the purpose of clearness I have shown the thermometer. I Anadditional resistance E may be connected in series with W by means of aswitch U,. By means of a further switch U.,, the thermometer may be outout of its branch, and a testing resistance P may be switched in. Thelatter is equal to the resistance of the thermometer at any suitableknown temperature. By means of a Switch U an additional resistance Z maybe switched in the branch of the galvanometer, whereby the sensitivenessof the galvanometer G can be varied at will. i

The current passing through the galva nometer is, other conditions notbeing altered,

a function of the resistance of the thermometer. When using a constantvoltage, the galvanometer can .therefore be used to directly indicatethe variations of the resistance of the thermometer, whereby also thetemperature of the latter will be indicated. Now, this method ofdirectly reading the peratures of the thermometer varying within smalllimits and causing a weak current topass through the galvanometer,while, when the variations of the temperature are large and the currentis strong, and therefore the displacement of the pointer of thegalvanometer is large, the measurements will not be very accurate. If,for example, the re- ,sistances of W, and W be equal, the zero point ofthe scale ,will be obtained by choostemperatures is sufficiently exactwith te-mmg the resistance of W, equal to that of the thermometer at acertain temperature. Now, for temperatures not considerably differingfrom the said temperature, the measurements will be exact. I If,however, the temperatures intended to be measured are considerablydiflerent from that of the zero position of the galvanometer, exactmeasurements can not be obtained. In using the system, it happens quitefrequently, that, for a certain range for example from 0 to 800centigrade,

exact results are not re uired, while for a certain interval, for exampe from 700 to 800 exact results are required. For the interv of from 0to 800 requiring rough results the aforesaid method will worksatisfactorily. In order to obtain good. results for the latter intervalof from 700 to 800, I add to the resistance W the further resistance E,the sum of the resistances W, E being equal to the resistance of thethermometer at a temperature near the interval of the exactmeasurements, viz. in the example stated, from 700 to 800. The sameresult can evidently also be obtained by v the resistance of one of theother branches, t ough the method explained appears to be the mostconvenient one. For obt the aforesaid results,the

voltage of the current supplied to the bridge a must be constant. Thismaybe obtained either by using a constant source of electricity, or byincluding in the supplying circuit a variable resistance B, when asource of variable vol is used. The said resistance R -may be usted soas to furnish the voltage required in the system by means of the testmgresistance P referred to above, which may be switched in the branch ofthe thermometer, while the latter is cut out. By varying the resistanceR until the pointer of the galvanometer is at the proper position thevolta'ge required in the system can easily'be ob- In order to obtain asufficiently constant voltage for continuous measurements, where arepeated adjustment would be troublesome, means are provided in my imroved system, whereb even when including the system in a hg ting circuitthe voltage of which constant y varies large limits,

an exact voltage can constantly be obtained.-

An exampleof such means is shown diagrammatically in Fig. 2. In thisexample a polarization cell A and iron resistances N, such as have beenused in combination with Nernst lamps, are included in the circuit. Asiswell 4 known in the art, the said resistances are able to balance volta central station is subjected to real changes, the indications'of thegalva-.

varying within lar e hmits, whereby wit certain limits, t e current doesnot change. Considerable variations of thevoltage of a certain durationare to a large extent absorbed by said resistances. However, as acurrent s'u plied from Past periodto the alance accor nometer wouldlikewise vary T said variations of the vol these oscillations, theconnected in shunt wit the bridge, whereb" the oscillations are entirelannihilate Practical tests have shown, t at with varia tions of thevoltage up to 20 per cent. the variations caused in the galvanometerbranch of the bridge do not amount to more than a few thousandths. Anydesired polarization cell may be used .in my system. 'Good reance willnow be lanzation cell A is sults have been obtained, for example, withcells comprising nickel electrodes. m 'potas-' sium or-sodium l e. T

An example 0' the art of my invention,

provi means to ba ance the resistance of the con uctor of thethermometer branch, is shown in Fig. 3. In the said exampletheresistance W, of the branch adjacent to the thermometer and galvanometerbranches is and the conductor of the test- J mg resistance P. A slidingcontact 0 con- I nected with one end of the conductor of the thermometerT and with thewgalvanometer is adapted to cut off equal lengths from-theloop ortion of the branches of the resistance and the testing resistanceP. Now, in order to ad'ust the system the thermome ter is switche off byrrieans of the switch U,, while the testing resistance P is switched inthe circuit. Thelatter is equal to'the resistance of the thermometer ata certain known temperature, I of 0 centi a The system will now be soad'usted t at no current passes through the alvanometer. If now thethermometer,

aving the tem erature corresponding to the resistance of P b ance of itsconductor be large, the pointer of the galvanometer will show adeviation. By adjusting the slid contact 0 so much resistded to theresistance W as is required ,to bring the pointer of the galvanometer toits former position. By this operation, simultaneously the resistance ofP-is increased b the amount of the resistance of the con uctor of thethermometer, so that it can afterwards be used for testing the systemwithout further adjustment.

(preferably at the temperature e switched in, and the resist-- Anotherexample of the means to balance I the resistance of the said conductoris illustrated in Fig. 4. In this example also a resistance isadded toW, and P WhlOh is e ual to that of the conductor. To effect this, ourconductors 1, 2, 3 and 4 are used which are connected in the system asshown in the said I figure. The latter example is particularly useful,where the resistance'of the conductor is subjected to' considerablevariations, caused for example by variations of the temperature. As theconductors 1, 2, and 3 are subjected to the same influences as theconductor 4, their resistances will be eiually' changed, whereby thevariations o the temperature of the said conductors do not exert anyinfluence on the system.

In Fig. 5 I have shown a system embodymg the elements explained indetail with re erence toI Figs. 1, 2 and 3, the function of all the artsbeing the same. The current supplie by the generator B is reduced to itspro er voltage by means of the rheostat R,- whi e the oscillationsoccurring in the supplying circuit are balanced by means of the ironresistance N and the polarization cell A.

I claim:

'1. In a system of electrically measuring temperatures, the combinationwith aWheatstone bridge, of a resistance thermometer included in one ofthe branches of said bridge,

a galvanometer included in the central branch of the bridgeand having ascale indicating the Variations of the temperature of said resistancethermometer, and an iron resistance connected in series with the source15 of electric current.

2. In a system of electrically measuring temperatures, the combinationwith a Wheatstone bridge, of a resistance thermometer included in one ofthe branches of said bridge, a galvanometer included in the centralbranch ofthe bridge and having a scale indicating the variations'of thetemperature of said resistance thermometer, an iron resistance connectedin series with the bridge, and a Eolgrization cell connected in shuntwith the In testimony whereof ,I have signed my name to thisspecification in the presence of two subscribing witnesses.

ERNST HAAGN.

Witnesses:

FRANZ HASSLACHER, ERWIN DIPPEL.

